Grid construction



Jan. 28, '1 958 7 L. c. WERNER 2,821,6 1

GRID CONSTRUCTION Original Filed June 4. 1951 i -Eg.- Jig? 58.

I INVENTOR.

Z. C l s riac r GRID CONSTRUCTION Leo C. Werner, Cedar Grove, N. L,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Original application June 4, 1951, SerialNo. 229,778, now Patent No. 2,648,797, dated August 11, 1953. Dividedand this application March 30, 1953, Serial No. 345,596

2 Claims. (Cl. 313350) This invention relates to electron dischargedevices, and in particular relates to structures for the controlelectrode therein, this application being a division of U. S. Patent No.2,648,797, issued August 11, 1953.

As is well known, the control electrode for electrical discharge tubesusually consists of a cage or grid formed by winding a wire or filamentof suitable material helically about two or more upright rods parallelto the central axis of the tube. In most types of tubes, the cathode ispositioned within this helical winding, and it is usually necessary tomaintain throughout the operative life of the tube a uniform andaccurate spacing of the turns of the helix, both between the turnsthemselves and between the turns and the cathode surface which the helixsurrounds. These considerations require some way of fastening thehelical winding, turn by turn, to its supporting rods; and such afastening poses a problem of very considerable difiiculty, particularlyin the case of high power or high voltage tubes.

In many such high voltage tubes, the electron emissive cathode consistsof a plurality of heated tungsten wires, extending parallel to thecentral axis of the tube and at uniform radial distance therefrom. Thecathode filaments may then be considered as elements of a cylindricalsurface. In such cases, the control electrode is usually supported onrods lying on the same radial planes of this cylinder as the respectivecathode filaments and at a slightly greater radial distance than thelatter. Thus in Fig. 2 of the drawings, the control electrode is a wirewound helically about four support rods which, respectively lie on thesame radial plane through the central axis of the tube as do the fourvertical filaments which constitute the cathode.

Inhigh power tubes the control electrode usually comprises a molybdenumwire and it might seem simple to spot weld the turns of this wire to thesupport rods; but it has been found in actual practice that thisprocedure was unsatisfactory and caused frequent breakage of themolybdenum wire. The above-mentioned practice was accordingly supersededby an expedient shown in Fig. 1 of'the drawings in which the turns 1 ofthe grid wire were held properly spaced apart along the support rod 2 bya helical wrapping 3 somewhat larger in diameter than the post 2.However, to insure that slight displacements of the grid wire 1 did notpermit it to slip past the turnsof the helix 3, it was necessary thatthe latter should extend radially inward toward the cathode filament forsome distance beyond the inner edge of the grid wire 1, as is shown inFig. 1. This inward projection naturally limits the minimum spacingwhich was possible between the grid wire 1 and the adjacent leg 4 of thecathode filament and was otherwise found unsatisfactory.

In its general aspect the present invention has for its object animprovement in the supporting structure for the grids of electricaldischarge tubes. More particularly, the present invention has for itsobject the securnited States Patch oing of the grid wire to itssupporting posts with greater reliability and less intrusion on thelimited spacing between the grid wire and the cathode filament than waspossible with control electrode structures of the prior art.

Still another object of this invention is to provide a supportingstructure for electrical discharge tube grids which can be madeeconomically and is susceptible of being carried out readily in factoryproduction.

Other objects of the invention will become apparent to those skilled inthe art to which it appertains both by direct reference thereto and byimplication from the context.

Referring to the accompanying drawings, in which like numerals ofreference indicate similar parts throughout the several views: 1

Figure 1 is a sectional view indicating a support structure for controlelectrodes upon which the present invention improves;

Figure 2 is a view partly in elevation and partly in section of a highpower electrical discharge tube having a control electrode structureembodying one form of this invention;

Figure 3 is a plan view of a control electrode embodying the arrangementof Fig. 2 with the grid convolution at the inside of the posts;

Figure 4 is a plan similar to Fig. 3, but with the grid convolution atthe outside of the posts;

7 Figure 5 is a perspective view of a post showing portions ofconvolutions carried by a post;

Figure 6 is a view in elevation of the support post used in theconstructions of Figs. 2 to 5, inclusive;

Figure 7 is a perspective view of a modified construction of post; and

Figure 8 is an elevation of a further modified construction of post.

Turning in detail to the drawings, Figure 1 has already been describedin sufiicient detail above. Referring to Figure 2, an electricaldischarge tube referred to generally by the reference numeral 11 is ofthe general type shown in U. S. Patent No. 2,398,608, issued April 16,1946, to the present applicant and H. I. Bailey and assigned toapplicants present assignee. Since this tube is fully described in theaforesaid patent, it is only necessary to state here that it comprisesan anode 12, a pair of tungsten cathode filaments, each of hairpin form,supported with their legs 4 parallel to and equi-distaut from thecentral axis of the anode 12, and a control electrode comprising amolybdenum wire 18 of helical form supported on four molybdenum posts 19which are in the same radial planes of the anode 12 as are the four legsof the cathode filaments 4. The cathode filaments 4 are held at theirlower ends in vertical posts 5 which are supported in turn from brackets6 affixed tovterminal posts 7 which are sealed vacuum-tight through aglass bowl 8 to which the anode 12 is likewise sealed. There are twoterminals 7 which are respectively connected through their brackets 6 toone end of each of the pair of cathode filaments 4, so that when thebrackets 7 are respectively connected to the two sides of a heatingcircuit current flows up one side of each cathode filament 4 and downthe other side to the other bracket 6 and terminal post 7.

The support posts 19 for the control electrode wire 18 are rigidly basedon an annular member 13 which may be supported from a post 14- at thecenter of the bowl 8 by a suitable bracket 15 which, for the sake ofsimplicity, in the drawing, is shown broken away in Fig. 2, since itforms no part of the present invention.

The upper end of the four posts 19 may be fastened to a top plate 16 tobrace them rigidly. The upper ends of the hairpin filaments 4 are heldspaced rigidly apart by a member'17 which is so thin'and light as torequire no outside support.

The invention contemplates the alternatives of gridsupporting posts 19either at the outside of. the grid-wire convolutions 18, as in Fig. 3,or at the inside thereof as in Fig.4. In both constructions, each post19 is provided with a series of substantially chordal grooves spaced atproper intervals along its length to correspond with the spacing desiredbetween the convolutions of the control electrode. The four posts 19thusgrooved, and cut to length so that the distances of the grooves fromthe support member 13 are sequentially proper to position the helicalgrid 18 relative to member 13, have the winding 18 installed in properposition in the manner which will be described more fully below. Thegrooves constitute ledges which receive, space .and support. theconvolutions of the grid at each crossing of the grid wire to theseveral posts. The grid wire 18 is then locked in position in thegrooves 20 by a helical binder 21 which may be preformed and slippedinto position on the post 19 with a rotary movement like a screw beingthreaded into position. The helical binder 21 may be considered aconvenient example of retaining means for retaining the convolutions ofthe grid wire upon its above-mentioned ledge.

In the first instance, of the construction of Fig. 3, to install thegrid wire 18. in position, it is first woundinto a helix with desiredspacing and internal diameter on a suitable mandrel. grooves 20, arethen respectively positioned at points spaced 90 apart on this mandrelwith the convolutions passing through said grooves and with the oifsetlower portions of the posts positioned in radial planes passing throughthe axis of the helix. The support member 13 may then be attached to thelower ends of the support rods or posts 19. The mandrel may then bewithdrawn and the binders 21 rotatively slid downward into position onthe four posts 19. The top plate 16 may then be attached to the upperends of the posts 19.

In the embodiment of the posts located internally of the grid-wireconvolutions as in Fig. 4, the grooves 20 in the support posts 19 whichcontain the helical grid wire 18 and form ledges therefor, are locatedin the radially outward faces of the latter. In this case, the supportrods or posts 19 may be assembled with the support member 13 before thehelical winding 18 is put in place. A mandrel having an outside diameterequal to that desired for the internal radius of the helical grid andprovided with four suitable grooves to receive the posts 19 may then beslipped into position through the central opening in the support member13. The wire 18 may be wound as a helix fitting in the grooves 20 in theposts, after which the mandrel is withdrawn. A helical binder wire 21may then be rotatively slid downward into place on each of the supportposts 19 in the same manner as has been described above, and againconstitutes a retaining means for retaining the convolution of the gridwire seated upon its ledge in assembled condition.

In accordance with a modification of the invention, the-support post maybe made of semi-tubular material of the form illustrated in Figures 7and 8 and designated by'numerals 25 and 26 respectively. At intervalsequal to'the desired spacing for the grid convolutions, thesupport posts25, 26 may be punched to strike out projecting tongues 27 which are bentinto an L-shape, as shown in Fig. 7. The outwardly projecting portionsof .these tongues constitute ledges for the grid wire where theconvolutions thereof cross the posts. After the posts 25 The rods orposts 19, having chordal or 26 are mounted on the support members 13 ina manner similar to that described for the posts 19 in Fig. 2, a mandrelprovided with suitable longitudinal channels for the posts 25 or 26 andhaving a diameter equal to that desired for the internal diameter of thehelical con trol electrode 18 may be'placed in position and the gridwire 18 wound in helical configuration. Then the posts can be slid ontothe mandrel in the channels thereof substantially vto place and spreadto engage therespective-convolutions of thegrid in the L-shaped tongues27 and upon the ledges formed thereby. The four support rods 25 or 26will, of course, have to be cut'to length properly to that the tongues.27 are each.positioned at the correct distance from the support members13 to sequentially engage the convolutions of the helical wire 18properly. After the .gridwire 18 is thus placed in position, theL-shaped tongues 27 may be bent back over the wire 18 therebyconstituting a retaining means for the convolution where located on theledge to hold it firmly in position. The mandrel may then be removedfrom the structure and the grid completed and installed in the dischargetube in the same way as in Fig.2. Where the spacing between convolutionsis sufficient,- the tongues may be aligned 'one above anotherlongitudinally of the post as shown in Fig. 7.

Fig. 8 shows a support rod 26 of the same shape in cross-section as thatdescribed in connection with Fig. 7, but in which the tongues 27 arerequired to be so closely spaced lengthwise of the support rod toaccommodate the axial-spacing of the grid wire 18, that.tongues 27 wouldinterfere with each other, if they extended parallel to the longitudinaldimension of the support rod. Hence in Fig.8, the tongues 27 are punchedat an angle to the longitudinal axis of the support rod, but as abovedescribed, said tongues again each constitute a ledge and a retainingmeans for the grid wire convolution where crossing the post.

I claim:

1. A support post for the control electrode of an electrical dischargetube comprising a linear member having L-shaped tongues struck uptherefrom, said tongues having portions constituting ledges and havingportions constituting retaining means extending substantially parallelto the longitudinal central axis of said member, and said ledges beingspaced apart along said member to receive successive turns of wireconstituting said control electrode.

2. A support post for the control electrode of an electrical dischargetube comprising a linear member having L-shaped tongues struck uptherefrom, said tongues having portions constituting ledges and havingportions constituting retaining means inclined in a directioncircumferentially of the electrode at a substantial angle thereto and tothe longitudinal dimension of said member.

ReferencesfCited in the file of this patent UNITED STATES PATENTS1,432,411 Payne Oct. 17, 1922 1,654,899 Schwerin Jan. 3, 1928 1,792,219Grebel Feb. 10, 1931 1,957,223 Murphy May 1, 1934 1,976,522 Rose Oct. 9,1934 1,994,307 Flaws Mar. 12, 1935 2,188,906 Lackey Feb. 6, 19402,686,885 Bailin Aug. 17, 1954 FOREIGN PATENTS 85,420 Austria Sept. 10,1921 192,592 Great Britain Feb. 8, 1923

